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The food web structure of a coastal fish community (western Dutch Wadden Sea) was studied based on stomach content data from samples collected between 2010 and 2018. In total, 54 fish species were caught and 72 different prey items were identified. Fish species consumed from only a few up to >30 different prey species, suggesting the presence of both opportunistic and more specialized feeders. We found no significant differences between years or switches in food source with fish size. The trophic positions of the Wadden Sea fish community ranged from 2.0 to 4.7, with most trophic positions above 3.0. In the past, (near)-resident species were the most abundant guild in spring, and juvenile marine migrants in autumn. At present, all guilds are pre sent in similar but low abundances. The (near)-resident community consisted of about 20 species that fed primarily on amphipod crustaceans, brown shrimps and juvenile herring. There was only a slight overlap in diet with the group of juvenile marine migrants (5 species of juvenile flatfishes and clupeids), whose preferred prey were copepods, polychaetes and brown shrimps. About 15 species of marine seasonal visitors showed an overlap in diet with both the (near)-resident and the juvenile marine migrants, especially for brown shrimps and to a lesser extent herring and gobies. Our results illustrate (1) the pivotal position of a few key prey species (amphipod crustaceans, brown shrimps, juvenile herring and gobies) for the coastal Wadden Sea fishes and (2) that the substantial prey overlap in the diet of some predators cannot exclude intra- and inter-specific competition among these predators.

Large-bodied sharks can be critical for coupling disparate habitats and food webs, which is considered central for ecosystem stability. Understanding the role of sharks and their associated predator–prey relationships across spatial scales is also integral to the development of multi-species ecosystem models. A combined stomach content ( n  = 212) and multi-tissue stable isotope (fast [liver; n  = 101] vs slow turnover [muscle; n  = 108]) approach was used to investigate the feeding ecology of the copper shark ( Carcharhinus brachyurus ) in the temperate waters of Southern Australia. Sharks were sampled from fishery catches over 3 years, during the austral spring–summer seasons and across three distinct regions. Stomach content analysis identified the copper shark as a generalist predator that consumes a diverse prey base dominated by Sepia novaehollandiae, Sepioteuthis australis , and Sardinops sagax (36%, 21%, and 18% IRI). Regional differences in diet composition were evident, although no size- or sex-based variation was identified. Isotope mixing models and regional food web bi-plots also revealed that S. sagax was the most important prey species, but temporal variation in diet was observed that matched known movements. The copper shark was estimated to be a primary piscivore, feeding at trophic level 4.49. Data on the feeding behaviour of copper sharks will provide vital inputs into future ecosystem-based fishery models and guide conservation and management of this important marine predator in temperate Southern Australian coastal waters.

Effective marine ecosystem monitoring is critical for sustainable management. Monitoring seabird diets can convey important information on ecosystem health and seabird–fishery interactions. The diet of breeding black-browed albatross (Thalassarche melanophris) has previously been assessed using stomach content analysis (SCA) or stable isotope analysis (SIA), but not both methods together. Combining dietary sampling approaches reduces biases associated with using single methods. This study combines SCA and SIA to study the diet of black-browed albatross chicks, with a specific focus on fishery discard consumption, at two Falkland Islands colonies (New Island 51°43′S, 61°18′W and Steeple Jason Island 51°01′S, 61°13′W) during two consecutive breeding seasons (2019 and 2020). SCA provided high taxonomic resolution of short-term diet and priors for stable isotope mixing models, with multiple measures of dietary items (e.g. numeric frequency N%, frequency of occurrence FO%). By contrast, SIA of down feathers provided a single and more integrated dietary signal from throughout chick development. Although the two methods disagreed on the dominant prey group (SCA—crustacean; SIA—pelagic fish), the complementary information suggested a chick diet dominated by natural prey (SCA: 74%–93% [FO], 44%–98% [N]; SIA: minimum 87%–95% contribution). Nonetheless, SCA revealed that a high proportion of breeding adults do take discards. We detected consistent colony-specific diets in relation to prey species, but not in relation to higher discard use. Overall, discard consumption was highest in 2020, the year characterised by the poorest foraging conditions. Our results have implications for fisheries management and future dietary studies assessing discard use.

Effective management of a rapidly increasing juvenile green sea turtle Chelonia mydas population necessitates an understanding of the foraging grounds utilized throughout ontogeny. We used stomach content (SCA) and stable isotope analyses (SIA) of multiple size classes of green turtles foraging along the middle (MTC) and lower Texas coasts (LTC) in the northwestern Gulf of Mexico to identify ontogenetic shifts in foraging behavior. Spatial differences in diet and habitat residency were examined based on samples gathered from live (n = 55) and deceased turtles (n = 114). Additionally, the isotopic composition of putative forage material within nearshore and inshore habitats was investigated to determine prey contribution to diet. Green turtle recruitment to neritic channel environments in Texas waters at sizes <25 cm straight carapace length (SCL) was established based on the presence of benthic macroalgae in the diet. Integration of SCA with SIA of carbon and nitrogen in scute material, as well as potential prey, revealed a subsequent inshore shift to seagrass beds before obtaining 35 cm SCL for turtles of the LTC, while turtles from the MTC exhibited considerable variation in size at transition. This study improves our understanding of the feeding ecology of green turtles within critical foraging grounds along the Texas coast.

Knowledge of the ecological roles of species within food webs and how their trophic interactions affect food web structure is critical to model management and conservation scenarios for species that are suffering high levels of anthropogenic pressure, such as hammerhead sharks. In this paper, we analyze the diet and trophic relationships of 4 sympatric hammerhead shark species using a combination of stomach content and stable isotope analyses. These species showed trophic similarities by sex and trophic dissimilarities by maturity stage. We found that the trophic niche of hammerhead species tends to be more similar within species than among them. This suggests that competitive interactions are more likely to occur between conspecifics than between congeneric individuals and highlights the potential different roles that these species can play within the food web structure. The intermediate to high trophic positions observed in Sphyrna corona, S. media, S. tiburo and S. lewini juveniles indicate mesopredator roles, whereas S. lewini subadults could be considered top predators. Our findings revealed multiple trophic interactions between hammerhead sharks and prey from different trophic levels, which could be critical for the structure and function of marine food webs.

Indo-Pacific lionfish Pterois spp. have recently invaded marine habitats throughout the western Atlantic, Gulf of Mexico, and Caribbean Sea. Their unusual hunting behaviour suggests that they could prey on most fish species within their gape size limits. However, few prey species have been identified so far due to the challenges of identifying partly digested prey. Moreover, it is not clear how well the identifiable diet reflects the unidentified portion. To address these issues, we DNA-barcoded unidentifiable fish items from the stomachs of 130 lionfish captured on Bahamian coral reefs. We identified 37 fish prey species, nearly half of which had not previously been recorded in this region. The total richness of lionfish prey fish recorded so far may represent up to ~54% of potential prey species on the study reefs. The relative importance of prey species in the visually identifiable diet portion, which was limited to 25% of prey items, differed from that in the ‘unidentifiable’ portion, which was largely resolved here with barcoding, weakening extrapolations from visual identification. The high diet resolution afforded by barcoding can increase our ability to predict the impacts of invasive predators on recipient communities.

With warming ocean temperatures, the abundance of blue whiting Micromesistius poutassou is increasing in the waters around Greenland. However, in this region, knowledge about the species’ trophic role in the ecosystem is scarce. Consequently, we investigated the diet composition and diel feeding behaviour of blue whiting in the north-eastern part of the Irminger Sea in Greenland waters by analysing their stomach contents and the vertical position/movements of their prey from zooplankton samples and hydroacoustic measurements. We collected the data during a designated experimental survey in July 2016 with repeated sampling at the same location. Results from the stomachs of 624 blue whiting individuals ranging from 22–39 cm long (total length) showed that the highest food intake took place from noon until late evening, with minimum feeding occurring in the morning. The most essential prey groups consisted of euphausiids, copepods, amphipods and fish, in that respective order. Regarding copepod prey, blue whiting had a strong affinity for Calanus hyperboreus and Paraeuchaeta spp. and showed potential for local depletion of these large copepods. On the other hand, the more abundant but smaller C. finmarchicus was almost absent in the fish stomachs, in contrast to findings in other regions. This new understanding provides an early indication of some of the emerging trophodynamics in the Irminger Sea and similar subarctic zooplankton communities with increasing numbers of blue whiting. Our results confirm the importance of accounting for diel and size-specific differences in blue whiting feeding when studying various aspects of its food intake.

Understanding the foraging ecology of marine predators is essential for ecosystem-based fisheries management. This study examined the diet of the narrow-barred Spanish mackerel ( Scomberomorus commerson ) in the Central Taiwan Strait using stomach content and stable isotope analyses integrated with an isotopic mixing model. A total of 1,733 specimens were collected between January 2017 and March 2022. Stomach content analysis revealed that 79.8% had empty stomachs, while the remainder mainly contained semi-digested fish remains. Among identifiable prey, composition varied by size and season. Sardinella lemuru , Decapterus spp., and Trichiurus spp. dominated the diet of smaller individuals, while larger fish primarily consumed Decapterus spp. and Mene maculata . Sardinella lemuru and Trichiurus spp. were more abundant in summer and autumn–winter, respectively. In the meanwhile, Decapterus spp. remained important year-round. Isotopic analysis further revealed that Sardinella lemuru , Etrumeus micropus , Decapterus macarellus and Penaeidae ( Metapenaeopsis barbata ) were dominant prey in smaller size classes, while Encrasicholina punctifer , D. macarellus , Evynnis cardinalis , Trichiurus spp. and Uroteuthis spp. were prevalent in intermediate and larger individuals. The estimated trophic position (3.8–4.3; mean = 4.0) confirms that S. commerson functions as a top predator with opportunistic feeding behavior. These findings improve understanding of regional trophic dynamics and support sustainable fisheries management in the Central Taiwan Strait.

Individual niche specialization (INS) is increasingly recognized as an important component of ecological and evolutionary dynamics. However, most studies that have investigated INS have focused on the effects of niche width and inter- and intraspecific competition on INS in small-bodied species for short time periods, with less attention paid to INS in large-bodied reptilian predators and the effects of available prey types on INS. We investigated the prevalence, causes, and consequences of INS in foraging behaviors across different populations of American alligators (Alligator mississippiensis), the dominant aquatic apex predator across the southeast US, using stomach contents and stable isotopes. Gut contents revealed that, over the short term, although alligator populations occupied wide ranges of the INS spectrum, general patterns were apparent. Alligator populations inhabiting lakes exhibited lower INS than coastal populations, likely driven by variation in habitat type and available prey types. Stable isotopes revealed that over longer time spans alligators exhibited remarkably consistent use of variable mixtures of carbon pools (e.g., marine and freshwater food webs). We conclude that INS in large-bodied reptilian predator populations is likely affected by variation in available prey types and habitat heterogeneity, and that INS should be incorporated into management strategies to efficiently meet intended goals. Also, ecological models, which typically do not consider behavioral variability, should include INS to increase model realism and applicability.

Psalidodon paranae is an endemic small Characidae from the Upper Paraná River ecoregion (Neotropical region, Brazil), where many watercourses are affected by anthropic activities. The Verde River (VR) was chosen as a model to study the feeding trends of P. paranae. Based on empirical observations, hypotheses were set concerning its occurrence, the environmental representativeness of its diet and the multifactors modulating ontogenetic, spatial, and temporal diet variations. To evaluate these hypotheses for the first time, an integrative approach was applied (modelling and multivariate techniques). Standardized samplings were performed monthly during one year at four sites. Influence of environmental variables on fish distribution was evaluated by means a general linear model. Stomach content analysis of P. paranae allowed the calculation of gravimetric frequency of consumed food categories. Ontogenetic, spatial, and temporal differences on diet were evaluated by means a permutational multivariate analysis of variance, and the influence of environmental variables on them with a canonical correspondence analysis. From the total of 301 specimens caught (4.6–13.4 cm total length range), 216 individuals of P. paranae presented stomach with contents. The species consumed 32 different food categories in VR, highlighting aquatic and terrestrial angiosperms, and beetles. The methods applied identified significative spatial and temporal differences in P. paranae diet as result of multifactors (palaeogeomorphology, abiotic, biotic, and anthropic) operating in the VR. Heterogeneity and complexity of VR and P. paranae occurrence and feeding trends evidenced that the opportunistic and generalist behavior lead to intrinsic patterns of each fish population at each watercourse.